1. Field of the Invention
The present invention relates to the processing of video data to be displayed. More particularly, the present invention relates to displaying video data stored in a memory in digital form.
2. Description of the Prior Art
As digital data processing has become more widespread and sophisticated, the need for displaying digital data in a more sophisticated manner has also increased. In this regard, the capability for displaying in color has been added and resolution has increased.
In data processing systems having a color capability, data to be displayed may be stored in an image memory in a display controller. Typically, each pixel to be displayed is represented by 8 bits of data in the memory. These 8 bits of data must eventually be employed to control the intensity level of the three electron guns (red, green and blue) in a cathode ray tube. If the 8 bits of data were used directly to control the guns, relatively little resolution would be possible with respect to the intensity level of each gun.
To overcome this problem, typically the display controller includes a video lookup table for each gun, each of which is addressed by the 8 bits from the image memory and may, typically, produce an output of 8 bits. These output bits are employed to control the corresponding gun of the cathode ray tube. Thus, with 8 bits of data, each gun is capable of being controlled to any one of 256 levels of intensity. With three video lookup tables each addressed by 8 bits, the capability exists to produce 16.8 million different combinations of intensity levels with the three electron guns. However, since the video lookup tables are addressed by only 8 bits, only 256 of these 16.8 million possible combinations are defined at the discretion of the video lookup table programmer.
The output of the video lookup tables are applied to a digital-to-analog converter which generates a voltage signal related to the digital output of the video lookup tables. These voltage signals are then transmitted from the display controller to the monitor where they are amplified and employed to drive the guns of the cathode ray tube.
As suggested above, data is transmitted from the controller to the monitor in the form of an analog voltage. In fact, interface standard RS-343A controls the nature of the signal sent to the monitor. This standard sets the maximum peak-to-peak voltage at 1 volt. With the standard, manufacturers are able to produce monitors which can be used with any display controller.
Thus, U.S. Pat. Nos. 4,107,780, 4,015,286 and 3,617,626 all teach display systems in which digital data is converted to analog form before being sent from a display controller to the display monitor. U.S. Pat. No. 4,317,114 to Walker teaches a display system in which data initially appears in digital form which is then converted to analog form. However, no indication is made as to the nature of the data transmitted from the controller to the monitor.